From what I've read, it seems this boiler is a nice display item for "how not to make a boiler." They should construct a new boiler to modern specs of staybolt spacing, etc, so that she may run full pressure.
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Thanks for posting this photo. While I was in Altoona last week, my uncle in Altoona did tell me the boiler made it back to Altoona. I didn't have time to go through the museum to see the boiler. FYI...the frame for the K4 is in the old portion of the Railroader's Museum (I saw the k4's frame and some of her hardware through the old museum doors).
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Going out on a limb here, perhaps risking my neck for defending this:
"How not to construct a boiler" isn't the point here. The PRR screwed up their engineering at one point or another, and somehow got away with it for decades. And that flawed engineering can be corrected. Kelley Anderson (Strasburg) has commented that NOT finding flawed engineering is more of a red flag than finding it...it's usually just not this bad.
"Needs a new boiler" is also incorrect. The ENTIRE 'problem area' is limited to the firebox wrapper, specifically the roof sheet. The spec plate thickness is 0.375", the bare minimum allowed, and no corrosion allowance was given. The roof sheet would need replaced due to wastage alone, as some areas are down to 0.340." The engineering flaw is that even with spec thickness, the staybolt pitch is too great to meet a safety factor of 4. Increasing the plate thickness would push the staybolt stresses beyond regulatory requirements. Replacing both the roof sheet and crown sheet with a corrected staybolt pitch, and a thicker roof sheet, will be the most likely solution. While they haven't published anything, I have a hunch that the museum may have already had the engineering done quietly.
The boiler barrel itself is fine and has a few decades of excursion service life left in it. Spec plate thickness is 1.000" and the lowest I've seen on her was 0.950." The steam dome course got patched ONLY because the dome never seated correctly, and the rivets holding the dome in place stressed the holes abnormally, cracking the plate in that area. Those problems have all been corrected already.
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